Engine valve actuation

A non-transitory, computer-readable storage medium storing computer program instructions that, when run on at least one electronic processor, cause the at least one electronic processor to control an electromagnetic valve actuator for at least one valve of an internal combustion engine, the electromagnetic valve actuator comprising:

• a rotor, a stator for rotating the rotor, an output for actuating the valve in dependence on rotation of the rotor, a mechanical energy storage device arranged to store energy in dependence on rotation of the rotor and release the energy to assist rotation of the rotor, and a phase varying device for varying a phase between the mechanical energy storage device and the output, the computer program instructions causing the at least one electronic processor to control the phase varying device to vary the phase between the mechanical energy storage device and the output.